Biological toxicity relates to the shape of asbestos fibres. The mesothelial cell appears to be a predominant target of the asbestos fibre – consequently leading to the disease ‘mesothelioma’. Understanding how the shape, chemical composition, and surface structure interact to result in a harmful biological agent is paramount to the study of prospective harmful fibrous materials in the future.
The long thin shape of an asbestos fibre may enhance its entry deep into the lung. Following inhalation, fibres of several micrometres in length can enter the respiratory airways, whereas other particles larger than 5 micrometres could not penetrate. Once in the lung – the long fibres may not be cleared by the bodies natural defence mechanism such as ‘macrophage clearance’ macrophages generally mop up foreign bodies, but scientists have discovered that certain stubborn asbestos fibres (such as needle-like shape) cannot be cleared by macrophages. These fibres may more easily migrate along tissue planes, lymphatic channels and make their way into the pleural space.
Animal studies show certain asbestos shapes induce mesothelioma
Asbestos shape has been considered to be a primary characteristic determining asbestos toxicity, i.e. ‘Stanton et al’ 1977, recognised size and shape as a major factor in inducing mesothelioma in animal studies. For instance – other materials with the same shape but different chemical composition share the ability to produce mesothelioma. Also – studies of asbestos fibres with a long thin shape were shown to be able to induce chromosomal abnormalities.
Studies of human epidemiological trials and lung mineral toxicity conclude that ‘amphibole’ asbestos fibres (crocidolite and amosite) are more predominantly associated with mesothelioma than chrysotile fibres. Amphibole fibres contain more iron; possess a higher aspect ratio, and their needle-like shape is more brittle.
Conclusion
Asbestos shapes have chemical differences. Physical properties are important in determining the toxicity of the fibre, predominantly – the fibres shape, surface reactivity and chemical composition.